Electromagnetic pole



Dec. 29, 1936. A. wlNTHER ELECTROMAGNETIC POLE original Filed uarcn '7, i934 original Filed March '7. 1954 2 sheets-sheet 2 m mw WM nehme 2a, 1936 `UNITED -sTA'rss 20.225 ELECTROMAGNETIC POLE Anthony Winther, Kenosha. Wis., assignor to- Martin P.Wlnther, trustee, Waukegan. lll.

Original No. 1,977,600, dated October `16, 1934, Serial No. 714.437, March 7, 1934. Application for reissue June 12, 1936, `Serial No. 84,911

8Clalms.

I'his invention relates to electro-magnetic poles, and with regard to certain more specific features. to such poles, particularly for eddy current electric clutches and the like.

| Among the several objects of'the invention may be noted the provision of a new and improved electro-magnetic pole` for increasing the eihciency of eddy current electric clutches and -similar machines: the provision of a device of io this class which shall reduce to a minimum the slip between the driving and driven elements of such clutches; the elimination in an eddy current clutch of the requirement for locking together the driving and driven members by means of a friction or Jaw `clutch when substantially direct drive vis required: and the provision of apparatus of the class described which shall be simple in form and dependable 1in operation. Other objects will be in part obvious and in part go pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements oi' parts which will be exemplined in the structures hereinafter gs described,'and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which is illustrated on of various possible embodiments of the invention. so Fig. 1 is a longitudinal section o! a device embodying the invention; Fig. 2 is a cross section taken on line 2-2 of Fig. 1, parts being shown in elevation; and,

Fig. 3 is an enlarged fragmentary' section illus- 85 trating certain principles of operation.

similar reference characters indicate corresponding parts throughout the several views of the drawings.

Reference is made herein primarily. to clutches 40 of the type using eddy current members of homogeneous materials such as steel rings o r drums, permitting variations in slip by regulating excitation of a magnetic member.

The principles also apply to any machines de- 46 pending forgoperation upon the production of eddy currents in atleast one of two relatively moving members. In Fig. 1 is shown such a device comprising a driver i to which is keyed an eddy current member t of homogeneous material such as steel and having a cup shape surrounding a driven electro-magnetic member 5, the latter being connected `to the driven member 1.

Pilot bearings l permit relative motion between 55 the eddy current member I and the electro-mag- -tric induction motors.

neue member s. s bearing n supports the dnven elements in a frame I3. the latter supporting brushes I5 whi'ch are connected to an outside circuit and bear on slip rings 2i. windings I1 on poles I9 of the magnetic member 5 are connected to the slip rings 2l and are thus energized. 'I'he current from the outside source thus energizes the coils I1 so that an electro-magnetic` eld emanates from or enters the poles I9, depending upon the direction of winding, and passes a gap between said poles and the eddy current member 3. Thus a magnetic drag is effected between the member 3 and the member 5 according to the intensity of the field. The weaker the field, the more is the slip because'of lower eddy currents and the less is the drag effect.

Heretofore, it has been the practice to increase the strength of the electro-magnetic field so as to reduce slippage and approach synchronism.

However, the synchronous condition was onlyr very approximate and it was the practice to use a friction or jaw clutch under the desired direct drive condition. For-example, see United States Patent 1,825,934 issued to J. Bing on October 6, 1931.

The usualmethod of making magnetic poles of this class in dynamos and the like is to decrease the iiux density crossing the air gap to a value much smaller than that permitted by the paramagnetic part of the circuit. This was done on the correct theory that the lower the density, the less ampere turns will be required to force the total ux across the air gap. On dynamos and motors having separate path inductors, this scheme produces the best and most elcient results. However. when using a solid rotor or the like, I have discovered the theory to be entirely different.

Referring to Fig. 3; if pole P were straight radially. that is, of equal cross sectional area laterally at B and C, the clutch would require a considerable excess of exciting current in coil D in order that the slip between pole face C and drum 3 might be brought to the low value of the order of that obtaining in the commercial run of elec- This slip is approximately of the order of one hundred feet per minute.

I have discovered that the greatest eiiiciency in the use oi.' exciting current on solid inductor eddy current clutches is obtained when the pole area at C is approximately 30% less than at B.

.For example. in a given-test. with a straight pole and paramagnetic pole cap having an area of greater than that of the bottom of the pole waist. the slip was 1500 feet per minute at section C when the flux density was of the order of 80,000 lines per square inch at section B. By removing the pole end of paramagnetic materials and extendin-g the pole waist C to form the identical air gap as used in the first test, and using a brass coil cap G, the slip with the same ampere turns as used before was reduced to 360 feet per minute. When the area at C was reduced to 30% less than at B, the slip was reduced to 30 feet per minute. On a Vten horsepower clutch operating at 1.150 R. P. M. this last-named slip Y amounts to only 10 R. P. M., or less than 1% of the power transmitted is lost. Hence there is no longer need for a friction clutch or jaw clutch as the drive is brought so close to synchronism as to make any loss negligible.

The cause of the above effect may be due to the fact that the slip factor is a function of the ux density at the air gap. The commonly acknowledged flux leakage at H across and between poles is 25% to 30% in a well designed field arrangement. As these magnets must be worked at a high density, coming near the saturation point of the steel, it seems that the leakage across H will prevent saturation of area C unless there .is sumcient taper to the pole piece to provide sumcient area'at B. The 'area of B must passV suflcient flux to practically saturate C and provide flux for the leakage path also.

On the. other hand if the taper of the pole is too steep, the leakage will increase from the pole waist sides J to the inductor surface K, and rob the active pole end C of usable flux.

I have found that there is a relation between the length of the pole and area at C and B. If the length of pole waist from section B at the base of the surrounding coil to section C at the end is less than the square root of the pole end area at C, the drive effects are quickly reduced as the relative distance B to C is reduced. In other words. the slip between driver and driven member is increased as the ratio of distance bey tween B and C to area of p'ole end C is reduced.

'I'he invention provides a means for more emciently producing eddy currents (in machines depending upon them for operation) by providing a steeper gradient of ux density at the boundaries of the waves of ux concentration which sweep around the member 3 under influence of the, relatively moving poles P. To do this it is not necessary that the electro-magnetic windings such as coils D be on the poles themselves.

They need only be so located in the apparatus that the generated flux path passes through the poles and member in which the waves of ux concentration are to move.

In view of the above. it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made y,in carrying out the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above dcrlption or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. In eddy current inductor apparatus, an electro-magnetic pole comprising a waist, said waist tapering inwardly from its base end to its gap end, a winding surrounding said waist, the length of said pole waste through said winding and to the section at the magnetic gap being greater than the square root of the pole end area at said gap.

2. An eddy current electric clutch comprising an/ eddy current member, an electro-magnetic member associated therewith, poles on said electro-magnetic member so related to the eddy current member as to form air gaps, said poles havingv pole faces at said gaps, said poles having waists, windings about said waists, said pole faces at said gaps being substantially 30% less in area than the areas of the poles at the bases of said windings.

3. An eddy current electric clutch comprising an eddy current member, an electro-magnetic member associated therewith, poles on said electrbfmagnetic member so related to the eddy current member as to form air gaps, said poles having pole faces at said gaps, said poles having waists, windings about said waists, said pole faces at said gaps being substantially 30% less in area than the areas of the poles at the bases of said windings, and the lengths of the pole walsts through the Vcoils to the pole faces being greater than the square roots of the pole end areas.

4. In an eddy current electric clutch. an eddy current member, an electro-magnetic member having poles, said poles having faces adjacent the eddy current member, and said poles having waists, electric windings on said waists, the relationship between the pole end areas and the pole base areas being such as to taper the poles through the waists down to the pole end areas such that the ilux leakage between poles is accommodated by the poles and effects substantially iiux saturation at the pole ends by means of the flux which passes through the eddy current member, and a non-magnetic collar about each pole end.

5 In an eddy current electric clutch, an eddy current member, an electro-magnetic member having poles, saidpoles having faces adjacent the eddy current member, and said poles having waists, electric windings on said waists, the relationship between the pole end areas and the pole base areas Vbeing such as to taper the poles through the waists down to the pole end areas such that -the flux leakage between poles is accommodated by the poles, and to eiect substantially flux saturation at the pole ends by means of the flux which passes through the eddy current member. 6. In an eddy current inductor, magnetic mem'- bers, said members being relatively movable, at least one pole on one of said members, at least one electro-magnetic coil, said coil linking at least one flux path passing through both magnetic members and including the pole, said pole having an end face adjacent the other magnetic member and having a sectional area spaced from said face. the relationshipbetween the pole-end area and said-sectional area being such as to reduce the pole section from said sectional area to the poleend area in a manner that all flux including leakage Il ux from the pole is accommodated by the pole at said sectional area, but at the same time to effect substantial flux saturation at the pole end by means only of the part of the ux which does not leak and which passes through both magnetic members nearl the pole-end area.

7. In an eddy current inductor, an eddy current member, a magnetic member, said eddy current and said magnetic members being relatively current member, said poles having sectional areas spaced from said faces, the relationship between the pole-end areas and said sectional areas being such as to taper the poles from said sectional n A areas to the pole-end areas in a manner that all flux including flux leakage between poles is accommodated by the poles at said sectional areas,

but at the same time to effect substantial i'lux saturation at the pole ends by means only of that part of the flux which passes both through the eddy current member and the pole-end areas.

8. In an eddy current inductor, an eddy current member, a magnetic member, said eddy current and said magnetic members being relatively movable, poles on said magnetic member, electric coils, said coils each linking at least one I iux path passing through the eddy current member and a pole, said poles having faces adjacent the eddy current member and spaced therefrom by a flux gap, and sectional areas in said poles spaced from the said faces, the relationship between the poleend areas and said sectional areas being such as to taper the poles from said sectional areas to the pole-end areas in a manner that all the flux including ux leakage between poles is accommodated by the poles at said sectional areas, and to effect substantial ux saturation at the pole ends by means o! the non-leaking part of the flux which passes both through the eddy current member and the pole-end areas.

ANTHONY WINTHER. 

